The HIV-1 envelope protein, gpl20, is a potent neurotoxin that evokes an aberrant pattern of glutamatergic activity in the synaptic network that forms in primary cultures of rat hippocampal neurons. gpl20 shed by HIV-l infected cells may contribute to the neurological impairment that frequently accompanies AIDS. Differences in the neurotropism of various HIV-1 strains in man and the observation that gpl2O elicits neurotoxicity in rodent models, suggest that the structural requirements for neurotoxicity are distinct from those required for infection. The structural elements of gp120 required to elicit neurotoxicity will be determined. HeLa cells will be transfected with various strain and mutant gpl20 genes and co-cultured with rat hippocampal neurons to assess the neurotoxicity of released gpl20. A model has been developed to test the hypothesis that specific patterns of synaptic activity result in neurotoxicity. Thus, aberrant patterns of electrical activity will be recorded with the patch-clamp technique and related to neuronal viability. This excitotoxicity model provides an assay suitable for evaluating the effects of drugs of abuse on glutamatergic synaptic transmission and neurotoxicity. Preliminary findings indicate that cannabinoids reduce this synaptic activity. The mitochondrion will be evaluated as a potential target for glutamate-induced calcium loads. Hippocampal neurons will be transfected with a mitochondrial directed apoaequorin gene. The calcium dependent luminescence of aequorin will be used to specifically measure mitochondrial calcium concentration. The role of mitochondrial damage in glutamate-induced cell death will be explored. In sensory neurons, the anti-HIV drug dideoxycytidine (ddC) decreases mitochondrial DNA (mtDNA) and alters calcium buffering. This observation may be relevant to the peripheral neuropathy that is a limiting side effect in the use of ddC for the treatment of AIDS. A series of novel nucleoside analogs will be tested for effects on mtDNA content and effects on calcium buffering in rat sensory neurons. These studies may identify compounds with anti-HlV activity that fail to exhibit neuropathic side effects. This proposal describes experiments that will provide a better understanding of the mechanism of gpl20-induced neurotoxicity. Molecular definition of the neurotoxic features of gpl20 will help identify its target in the CNN. The actions of gp120 on the synaptic network will determine the electrophysiological mechanism of neurotoxicity and the synaptic effects of abused and potentially neuroprotective drugs. Cellular studies will address directly, the mitochondrion as a potential target for glutamate and nucleoside-induced neuronal death.